The critically endangered pulmonate marine mollusc, Siphonaria compressa, is the smallest of the Siphonariidae (4-4.5 mm shell length) and lives only on eelgrass leaves near low water of spring tide in the Knysna estuary and Langebaan Lagoon, South Africa. The species exhibits indeterminate growth. Mating has been observed between adult individuals but exchange of spermatophores has to be confirmed. The limpet has a relatively short life cycle and releases completely metamorphosed juveniles from a protective spawn packet after 13 days at 25ºC and 18 days at 17ºC incubation. An attempt is made to assess generation time using growth in laboratory held individuals matched to the von Bertalanaffy growth function, and supported by sampling and analysis of natural populations during spring and summer. A measure of support has been found for the laboratory growth model. Early attempts are made to suggest reasons for, and the possible evolution of, the miniaturization shown by S. compressa.